"The accelerated inspections are being performed out of an abundance of caution and are expected to be completed over the next 30 days. The accelerated checks are ultrasonic inspections of fan blades of the CFM56 engines," the airline said.

The US Federal Aviation Administration also said it would order the inspection of 220 jet engines, while makers CFM said in a statement that it was supporting the investigation.

National Transportation Safety Board chairman Robert Sumwalt said a preliminary investigation found an engine fan blade was missing, having apparently broken and there was metal fatigue at the point where it would usually be attached.